Meetings, appointments, allday events, and event announcement count as busy time on your schedule. If the calendar doc is flagged "Mark private" it stays busy. With the flag "Mark available" there won't be an entry in the busytime.nsf. Anniversaries and reminders do not count as busy ...

Sets how long (in years) new anniversary entries will repeat. To set this preference, click File Preferences, and then click Calendar and To Do. On the Entries tab, enter a number (in years) for Repeat duration for anniversaries. The next time you create an anniversary, it will repeat for that ...